Calcium
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Calcium plays an essential role in many cell functions:
• Intracellular in muscle contraction and glycogen metabolism • Extracellular in bone mineralization • In blood coagulation and in transmission of nerve pulses.
Calcium is present in plasma in three forms:
free, bound to proteins or complexed with anions as phosphate, citrate and bicarbonate.
Decreased total calcium levels can be associated with
diseases of the bone apparatus (especially osteoporosis), kidney diseases (especially under dialysis), defective intestinal absorption and hypoparathyroidism
Increased total calcium can be measured in
hyperparathyroidism, malignant diseases with metastases and sarcoidosis.
Method
Photometric test using arsenazo III
Reagent:
Phosphate buffer 8-Hydroxyquinoline-5-sulfonic acid Arsenazo III
Specimen
Serum, heparin plasma or urine
Wavelength
650 nm, Hg 623 nm
Conversion factor
Calcium [mg/dL] x 0.2495 = Calcium [mmol/L] Calcium/U [mg/24 h] x 0.025 = Calcium/U [mmol/24 h]
Reference Range
Plasma or serum: 8.6 – 10.3 mg/dL (2.15 – 2.57 mmol/L) Urine [1]: Women < 250 mg/24 h (6.24 mmol/24 h) Men < 300 mg/24 h (7.49 mmol/24 h)
Principle
Calcium with arsenazo III at neutral pH yields a blue colored complex, whose intensity is proportional to the calcium concentration. Interference by magnesium is eliminated by addition of 8-hydroxyquinoline-5-sulfonic acid.